Nasa's Cassini spacecraft is headed toward its death plunge into Saturn, following a final distant flyby of the planet's giant moon Titan.

A last course correction by the probe saw it pass 73,974 miles (119,049 km) above the moon's surface, setting it on a trajectory that will end in its 'death dive' into the gas giant on Friday.

The encounter has been called 'the goodbye kiss' by mission engineers, because it provides a gravitational nudge that will send the spacecraft toward its dramatic ending in the planet's upper atmosphere.

On Thursday Cassini will send its last images of Saturn to Earth. Nasa expects to lose contact with Cassini at 7.45am EST (12.45 pm BST) on Friday.

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Nasa's Cassini spacecraft is headed toward its plunge into Saturn, following a final distant flyby of the planet's giant moon Titan (artist's impression). A last course correction by the probe saw it pass 73,974 miles (119,049 km) above the moon's surface, setting it on a trajectory that will end in its 'death dive' into the gas giant on Friday

TIMELINE OF DEATH DIVE FOR CASSINI

September 14, 3:58 pm ET., Cassini’s cameras take their last pictures.

September 14, 4:22 pm ET., Cassini’s last batch of data—including those last pictures—begin streaming back to Earth.

NASA plans to post raw images online as they are received. Earth will start receiving those signals at 5:45 pm ET.

September 15, 3:14 am ET., The spacecraft rolls into position to collect atmospheric data during the descent.

September 15, 6:31 am ET., Cassini enters Saturn’s atmosphere.

September 15, 6:32 am ET., Cassini’s antenna points away from Earth, leading to a loss of signal. Shortly afterwards, the spacecraft is vaporized.

September 15, 7:00 am-8:30 am ET, NASA livestreams the scene at mission control at NASA JPL, with live commentary about the end of the mission.

September 15, 7:55 am ET., Earth registers the loss of signal, indicating the end of Cassini.

Cassini has made hundreds of passes over Titan during its 13-year tour of the Saturn system, including 127 precisely targeted encounters, some at close range and some, like this one, more distant.

The spacecraft is scheduled to make contact with Earth at 9:19 pm EST today (2.19 am Wednesday BST).

Images and other science data taken during the encounter are expected to begin streaming to Earth soon after.

Navigators will analyse the spacecraft's trajectory following this downlink to confirm that Cassini is precisely on course to dive into Saturn at the planned time, location and altitude.

The geometry of the flyby will cause Cassini to slow down slightly in its orbit around Saturn.

This will lower the altitude of its flight over the planet so that the spacecraft will go too deep into Saturn's atmosphere to survive, because friction within the atmosphere will cause Cassini to burn up.

'Cassini has been in a long-term relationship with Titan, with a new rendezvous nearly every month for more than a decade,' said Cassini project manager Earl Maize at Nasa's Jet Propulsion Laboratory in Pasadena, California.

'This final encounter is something of a bittersweet goodbye.

'But, as it has done throughout the mission, Titan's gravity is once again sending Cassini where we need it to go.'

Cassini is ending its 13-year tour of the Saturn system with an intentional plunge into the planet to ensure Saturn's moons, in particular Enceladus, with its subsurface ocean and signs of hydrothermal activity, remain pristine for future exploration.

The spacecraft's fateful dive is the final beat in the mission's Grand Finale, 22 weekly dives. begun in late April, through the gap between Saturn and its rings.

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As Nasa's Cassini spacecraft draws ever closer to the dramatic end of its mission, it has been sending back some stunning images of Saturn.

An image taken with Cassini's narrow-angle camera in June has been released, which shows the intricate wave structure of Saturn's rings.

The image was released just days before Cassini began it last orbit of Saturn, with the craft finally ending its historic mission.

Cassini's last orbit begins this week on September 9. On September 14, the probe will take its final images of Saturn, snapping images of the gas giant's hexagon-shaped vortex at its north pole as well as its moons Titan and Enceladus

This view from Cassini spacecraft shows a wave structure in Saturn's rings known as the Janus 2:1 spiral density wave. Resulting from the same process that creates spiral galaxies, spiral density waves in Saturn's rings are much more tightly wound. In this case, every second wave crest is the same spiral arm which has encircled the entire planet multiple times

JANUS 2:1 SPIRAL DENSITY WAVES

Spiral density waves result from the same process that creates spiral galaxies, but are much more tightly wound.

In this case, every second wave crest is actually the same spiral arm which has encircled Saturn multiple times.

The Janus 2:1 spiral density wave is particularly remarkable because Janus – the moon that generates it – is in a strange orbital configuration.

Both Janus and Epimetheus (another of Saturn's moons) share almost the same orbit, and trade places every four years.

Each time those orbit swaps take place, the ring at this location responds, creating a new crest in the wave.

While Epimetheus also generates waves, these are swamped out by the waves from Janus – the larger of the two moons.

The image was taken on June 4, and shows a wave structure in Saturn's rings, known as the Janus 2:1 spiral density wave.

Spiral density waves result from the same process that creates spiral galaxies, but are much more tightly wound.

In this case, every second wave crest is actually the same spiral arm which has encircled Saturn multiple times.

In a post about the image, a spokesperson for Nasa said: 'This is the only major density wave visible in Saturn's B ring.

'Most of the B ring is characterised by structures that dominate the areas where density waves might otherwise occur, but this innermost portion of the B ring is different.'

While the image gives the illusion that the ring plane is tilted away from the camera towards the upper-left, this is not actually the case.

The Nasa spokesperson added: 'Because of the mechanics of how this kind of wave propagates, the wavelength decreases with distance from the resonance.

'Thus, the upper-left of the image is just as close to the camera as the lower-right, while the wavelength of the density wave is simply shorter.'

The Janus 2:1 spiral density wave is particularly remarkable because Janus – the moon that generates it – is in a strange orbital configuration.

Both Janus and Epimetheus (another of Saturn's moons) share almost the same orbit, and trade places every four years.

While the image gives the illusion that the ring plane is tilted away from the camera towards the upper-left, this is not actually the case. A Nasa spokesperson said: 'Because of the mechanics of how this kind of wave propagates, the wavelength decreases with distance from the resonance. Thus, the upper-left of the image is just as close to the camera as the lower-right, while the wavelength of the density wave is simply shorter'

Each time those orbit swaps take place, the ring at this location responds, creating a new crest in the wave.

The Nasa spokesperson said: 'The distance between any pair of crests corresponds to four years' worth of the wave propagating downstream from the resonance, which means the wave seen here encodes many decades' worth of the orbital history of Janus and Epimetheus.'

While Epimetheus also generates waves, these are swamped out by the waves from Janus – the larger of the two moons.

Nasa also released the highest-resolution colour images of any part of Saturn's rings to date, showing a portion of the inner-central part of the planet's B Ring.

The first image, taken on July 6, is a natural colour composite, created using images taken with red, green and blue spectral filters.

And the second is a colour-enhanced version, in which blue colours represent areas where the spectrum at visible wavelengths is less reddish, and red colours represent areas that are spectrally redder.

Analysis of additional images from this observation, taken using infrared spectral filters sensitive to absorption of light by water ice, indicates that the areas that appear more visibly reddish in the colour-enhanced version are also richer in water ice.

Last week, Nasa also released a stunning 'spacecraft's eye' view over Saturn's moon Enceladus.

The video stitches together images captured by the craft's narrow-angle camera, and offers a first-person perspective of the Aug 1 flyby, showing the relative motion of Cassini and the icy moon from about 112,000 miles (181,000 km) above.

The new view is a change from the typically static Cassini observations that have been released over the years.

It uses six images, taken with filters that allow infrared, green, and ultraviolet light, according to Nasa.

Yesterday, Nasa also released the highest-resolution colour images of any part of Saturn's rings to date, showing a portion of the inner-central part of the planet's B Ring. The first image is a natural colour composite, created using images taken with red, green and blue spectral filters

The second image is a colour-enhanced version, in which blue colours represent areas where the spectrum at visible wavelengths is less reddish (meaning the spectrum is flatter toward red wavelengths), and red colours represent areas that are spectrally redder (meaning the spectrum has a steeper spectrum toward red wavelengths)

These make for the red, green, and blue components in the resulting movie.

'The heavens often seem vast and unchanging as seen from Earth, but movement in the skies is the norm,' Nasa explains.

'The relative motions of both Cassini and Enceladus over a 15-minute period create the movement seen in this movie sequence.'

The Cassini space probe is approaching its final orbit between Saturn and its rings before its fiery plunge into the gassy planet.

The craft is now undertaking the last of its so-called 'Grand Finale' orbits, each bringing the probe closer to its long-awaited death dive.

This view of Saturn, taken by the Cassini probe, shows the planet's northern hemisphere in 2016. The craft is now undertaking the last of its so-called 'Grand Finale' orbits, each bringing the probe closer to its long-awaited death dive

Cassini's last orbit began last week on Saturday September 9, with the craft finally ending its historic 13-year mission six days later with a dive directly into Saturn's atmosphere.

Saturday's orbit sent the craft through the outermost layers of the planet's atmosphere, passing just 1,680 kilometres (1,043 miles) above the clouds.

Two days later Cassini made a final, 119,049-kilometre (73,973-mile) flyby of Saturn's largest moon Titan, causing the craft to slow down and re-position its orbit for its death dive.

Cassini has been probing Saturn, the sixth planet from the sun, and its entourage of 62 known moons since July 2004, providing enough data for almost 4,000 scientific papers. Pictured are the number of orbits and flybys the craft has performed over the past 13 years of research

This image of Saturn's rings was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan 28, 2016. Cassini's final dive will end a mission that provided groundbreaking discoveries that included seasonal changes on Saturn, the moon Titan's resemblance to a primordial Earth, and a global ocean on the moon Enceladus with ice plumes spouting from its surface

On September 14, the probe will take its final images of Saturn, snapping images of the gas giant's hexagon-shaped vortex at its north pole as well as its moons Titan and Enceladus.

The probe will then turn its antennae toward Earth, transmitting data until the final moment before it burns up as it heads straight into the gas giant's crushing atmosphere on September 15.

Cassini's final dive will end a mission that provided groundbreaking discoveries that included seasonal changes on Saturn, the moon Titan's resemblance to a primordial Earth, and a global ocean on the moon Enceladus with ice plumes spouting from its surface.

'The mission has been insanely, wildly, beautifully successful, and it's coming to an end in about two weeks,' Dr Curt Niebur, Cassini program scientist, said on a telephone conference call with reporters last week.

Last week, Nasa shared a stunning new view of Saturn's turbulent clouds, captured the day Cassini first began its Grand Finale. The breathtaking photo shows the swirling clouds 'on top of the world' at the ringed planet just weeks before Saturn's northern summer solstice

THE 'GRAND FINALE'

Cassini has circled Saturn for 13 years since reaching its orbit in 2004, spearheading remarkable discoveries about the ringed planet and its icy moons – but now, it's running low on fuel.

On April 22 the spacecraft began to transition into its grand finale orbits, taking one last close flyby of Saturn's massive moon Titan.

Titan's gravity bent Cassini's flight path, causing the orbit to shrink until it was on course to pass between Saturn and the inner edges of its rings.

Cassini then began the first of 22 dives through an unexplored gap before it ultimately plunges through the skies of Saturn to end its mission as 'part of the planet itself.'

Cassini's mission will officially terminate on September 15, after a planned plummet through Saturn's atmosphere.

And, all the while, it will transmit data from several instruments until the signal is finally lost.

Cassini's final photo as it heads into Saturn's atmosphere will likely be of propellers, or gaps in the rings caused by moonlets, said project scientist Dr Linda Spilker.

The spacecraft will provide near real-time data on the atmosphere until it loses contact with Earth at 7:54 am ET (12:54 am BST) on September 15, Nasa said.

Dr Spilker said Cassini's latest data on the rings had shown they had a lighter mass than forecast.

That suggests they are younger than expected, at about 120 million years, and thus were created after the birth of the solar system, she said.

During its final orbits between the atmosphere and the rings, Cassini also studied Saturn's atmosphere and took measurements to determine the size of the planet's rocky core.

Cassini has been probing Saturn, the sixth planet from the sun, and its entourage of 62 known moons since July 2004, providing enough data for almost 4,000 scientific papers.

Since the craft is running low on fuel, Nasa is crashing it into Saturn to avoid any chance Cassini could someday collide with Titan, Enceladus or any other moon that has the potential to support indigenous microbial life.

By destroying the spacecraft, Nasa will ensure that any hitchhiking Earth microbes still alive on Cassini will not contaminate the moons for future study.

Last week, Nasa shared a stunning new view of Saturn's turbulent clouds, captured the day Cassini first began its Grand Finale.

In a movie stitching together 21 images taken with Cassini's wide-angle camera, Nasa reveals a look at the entirety of the main rings. The images were taken over a period of roughly four minutes on August 20, 2017

THE SCALE OF SATURN

When it comes to space, it isn't always easy to understand how big objects really are.

To put things into perspective, if Earth was the size of a tennis ball, the moon would be the size of a marble.

Saturn would be the size of a beach ball and the sun would be the length of seven football fields away from Earth.

The breathtaking photo shows the swirling clouds 'on top of the world' at the ringed planet just weeks before Saturn's northern summer solstice – a period soon to be followed by years of darkness.

Cassini began the first of its final five orbits mid-August, bringing it closer to Saturn than ever before.

Images from its August 20 dive now offer a mesmerising 'inside out' perspective from the gap between the planet and its rings.

In a strikingly dynamic photo captured on April 26, 2017 – the day it approached Saturn for its first dive – Cassini observed the planet's north pole as it remained bathed in sunlight, from about 166,000 miles away.

But soon, the region will be enveloped in darkness.

Nasa's Cassini space probe (artist's impression) is approaching its final orbit between Saturn and its rings before its fiery plunge into the gassy planet. The craft is now undertaking the last of its so-called 'Grand Finale' orbits, each bringing the craft closer to its long-awaited death dive

'Although the pole is still bathed in sunlight at present, northern summer solstice on Saturn occurred on May 24, 2017, bringing the maximum solar illumination to the north polar region,' Nasa said.

'Now the sun begins its slow descent in the northern sky, which eventually will plunge the north pole into Earth-years of darkness.

'Cassini's long mission at Saturn enabled the spacecraft to see the sun rise over the north, revealing that region in great detail for the first time.'